1. Field of the Invention
This invention relates generally to the so-called silkscreen printing art and more particularly to an improved mounting assembly for removably mounting a stencil screen stretch frame in a silkscreen printing press.
2. Discussion of the Prior Art
The prior art of stencil screen printing, often referred to as silkscreen printing, is well known and widely used for a wide variety of printing applications. Briefly stated, silkscreen printing, or stencil screen printing as it will be referred to in this disclosure, is performed with the aid of a stencil screen to which a stencil pattern is applied in any convenient way. Silk cloth was originally used as the stencil screen and hence the name silkscreen printing. A variety of other stencil screen materials have been developed, however, and are used today although the name silkscreen printing persists.
In the stencil screen printing process, the stencil screen is stretched across the open side of a screen stretch frame and placed with one side of the screen in contact with the article to be printed. A suitable printing ink, which may be a true ink, paint, dye, or other printing medium, is spread across the opposite side of the screen. This ink is forced through the screen onto the article to be printed by means of a squeegee to reproduce on the article the stencil pattern on the stencil screen. Multicolor screen prints may be produced by performing a number of successive stencil screen printing operations with different color printing inks.
Commercial stencil screen printing is performed on a stencil screen printing press in which the various printing operations occur automatically or semi-automatically to permit high-volume production. One such stencil screen printing press is a cylinder screen printing press. The present invention will be described in relation to such a cylinder screen printing press although it will become apparent as the description proceeds that the invention may be adapted to other types of screen printing presses.
Simply stated, a cylinder screen printing press has a carriage support for mounting a stencil screen stretch frame containing a stencil screen and means for reciprocating the screen frame and its stencil screen edgewise in the plane of the screen through a printing stroke in one direction and a return stroke in the opposite direction. Below the carriage is a rotatable cylinder which is substantially tangent to the plane of the stencil screen within a zone of tangency which is referred to herein places as a printing zone. The cylinder rotates in one direction in synchronism with edgewise movement of the stencil screen and screen frame through their printing stroke so that the surface of the cylinder and the stencil screen move in unison in the same direction through the zone of tangency, i.e., the printing zone, during each printing stroke of the stencil screen.
Sheets to be printed are fed in succession to the cylinder by an infeed mechanism. Each sheet is held to the cylinder by vacuum or other means and rotates with the cylinder through the printing zone in unison with movement with the stencil screen through its printing stroke.
During operation of the cylinder screen printing press, ink is applied to the side of the stencil screen opposite the cylinder during each return stroke of the screen and its frame. During the following printing stroke of the stencil screen and its frame, a squeegee engages the screen approximately along the printing zone and forces the ink through the screen onto the underlying sheet which is currently moving with the cylinder through the printing zone to reproduce on the sheet the stencil pattern on the stencil screen. An outfeed mechanism strips the printed sheet from the cylinder and feeds the sheet from the machine.
The existing cylinder screen printing presses have one deficiency which this invention overcomes. This deficiency resides in the manner of mounting the stencil screen stretch frame in the press. In the existing cylinder screen presses, the screen frame is mounted on the reciprocating frame carriage by means of mounting brackets which are welded or otherwise permanently and rigidly attached to the screen frame and are bolted to the carriage. This method of mounting the screen frame in a cylinder screen printing press has several disadvantages.
First, the removal and replacement of a screen frame requires unbolting and bolting of the several frame mounting brackets from and to the printing press carriage. Secondly, the overall cost of the screen frame and its welded mounting brackets is relatively high. Thirdly, the mounting brackets, projecting as they do from the screen frame, render the frame difficult to handle and stack. Moreover, these mounting brackets often incur damage during handling and stacking.